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\noindent{\bf 19.  LONG RANGE CONSIDERATIONS}
\medskip
heat death, interstellar travel, transformation of
humanity by ai, exploration and occupation of the 
universe, occupation of the solar system,
population growth, long range resource system
George O. Smith and the matter duplicator

	In the main this book is about short and medium term opportunities
and problems for humanity, especially Americans.  However, the long term
future of humanity raises some interesting questions.

\noindent\underbar{The Heat Death}

	Ever since the formulation of the first and second laws of
thermodynamics in the nineteenth century, it has seemed scientifically
probable that the universe will eventually "run down", and life will
become impossible.  The discovery that the stars were maintained by
nuclear reactions made possible the first estimates of how long this
would take.  Our sun is good for several billion years without any
action on our part.  Other suns in our galaxy will last longer, and
we can imagine humanity moving to them.  Three questions arise:

\item{1.}Is the heat death really inevitable?  While it can be put
off by human action, unless present science is mistaken, it is inevitable.

\item{2.}Given that it is inevitable, is any human activity meaningful?
We don't want to go into this kind of philosophy, but will content ourselves
with a short answer.  Humans individually find plenty worth doing, even
though their lives are limited and so will the human race as a whole.
Of course, some theories of the "meaning" of individual lives are based
on the idea that the species is eternal, but it seems doubtful that
most individuals base their own lifetime activities on any such theory.
Pursuing the analogy with an individual further, it seems likely that
humanity will attempt to survive as long as possible.

\item{3.}How long can humanity survive and by what means?  Except
for possible immediate emergencies, serious consideration of this
question can be postponed for at least a billion years.  Therefore,
anything we say or do about it now is for our own amusement.

	Our sun is good for some billions of years, but we might have
to move closer unless we find some way of stoking it.  Material can be
collected to form new stars, but if our descendants wish to survive a
very long time, they may find it wasteful to expend the energy in stars
that radiate in all directions.  The very same conversion of hydrogen
to helium that powers the stars, can be used in fusion reactors to
produce energy as needed.  Economical use of hydrogen would give a factor
of a million to a billion in the length of time humanity can survive, i.e.
it might make 10\%518\%1 years possible.

	However, according to present theory most of the energy in the
universe is gravitational, and we can convert mass to energy by lowering
it into black holes.  At present rates of human consumption of energy,
our galaxy is good for expansion into space, varieties of human society,
varieties of human

\noindent\underbar{Getting control of the environment}

	In human history many natural catastrophes have occurred, but
they have all been localized.  Humanity as a whole has not suffered.

	In the history of the planet there have been planet wide
catastrophes, but they seem to occur at intervals of some tens of millions
of years.  Thus we are talking about intervals permitting tens to hundreds
of planet wide catastrophes in the history of the planet, but at intervals
that are a thousand times human history so far.

	My opinion is that humanity will try to survive for billions of
years, and therefore it is interesting to think about the nature
of the catastrophes and how humanity can avoid them.  However, serious
planning is not called for because of the time scale.  Another hundred
years of scientific and technological development will make any present
plans of historical interest only.

	However, let's begin with ice ages.  These don't seem to be
planet wide catastrophes, but they occur much more frequently ---
at intervals of tens of thousands of years.  There isn't total scientific
agreement on the cause, but the leading theory is the Milankovitch
astronomical cycle involving periodic changes in the earth's orbit around the
sun.  The Northern Hemisphere gets less sun during part of this cycle,
and hence there are ice ages.  What can we do about it?

	There are several possibilities.  The first is to sprinkle
soot on the ice in summer so it will melt faster.  The second is
to change the composition of the upper atmosphere so as to produce
a greenhouse effect --- the very effect that people are presently
worrying about making the earth too hot.  Of course, creating
a greenhouse effect, say by putting more freon gas into the stratoshere,
had better be done carefully, i.e. with an understanding of how
much freon will prevent the ice age without getting the planet too
hot.  We'd better also understand how to get rid of it again if it
doesn't dissipate by itself soon enough as presently seems most likely.
All this understanding will almost certainly be available long before
it is required.

	More generally, our descendants will want to establish control
over the temperature of the planet.  Most likely, they will decide
that the present distribution isn't optimal, and once they work out
the political problem of who gets what benefits, they will revise
it substantially.

	The major extinctions don't seem to be caused by ordinary
ice ages.  One leading theory is that the impact of a comet caused
the mass extinction 65 million years ago at the boundary between
the Cretaceous and Tertiary eras.  This extinction wiped out most
species.  Our ancestors, the mammals, did well by it.

	It seems likely that a comet can be prevented from striking
the earth provided we have enough warning to push it out of the
way with nuclear explosions.  Humanity would also survive it striking
the earth provided it was no worse than the hypothetical Cretaceous-Tertiary
comet.  The reasoning is like that concerning the far worse fictional
catastrophe of the sun going out.
\bye